1. Field of the Invention
The present invention relates to the manufacturing of unipolar components in vertical monolithic form. More particularly, the present invention relates to components such as Schottky diodes or MOS transistors made in vertical form in silicon substrates.
2. Discussion of the Related Art
In the manufacturing of unipolar components, opposite constraints have to be reconciled. Unipolar components must have as small a resistance (Ron) as possible when on, while having as high a breakdown voltage as possible when reverse biased. Minimizing the on-state resistance of a unipolar component requires minimizing the thickness of the less doped layer and maximizing the doping of this layer. However, to obtain a high breakdown voltage requires maximizing the thickness of the less doped layer and minimizing the doping of this layer. It is thus necessary to find a compromise between a high breakdown voltage and a reasonable on-state resistance.
An object of the present invention is to provide a novel method of manufacturing unipolar components of vertical type.
Another object of the present invention is to provide such a manufacturing method for a novel structure of unipolar components of vertical type that has a higher breakdown voltage.
To achieve these and other objects, the present invention provides a method of manufacturing a unipolar component of vertical type in a substrate of a first conductivity type, including the steps of:
forming trenches in a silicon layer of the first conductivity type;
coating the lateral walls of the trenches with a silicon oxide layer;
filling the trenches with polysilicon of the second conductivity type; and
annealing to adjust the doping level of the polysilicon, the excess dopants being absorbed by the silicon oxide layer.
The present invention also provides a unipolar component of vertical type including, in a layer of a first conductivity type, trenches filled with polysilicon of the second conductivity type, the lateral walls of the trenches being coated with a silicon oxide layer and the polysilicon doping being adjusted to be substantially equal to that of the layer of first conductivity type.
According to an embodiment of the present invention, the component is a Schottky diode and the trenches are formed in a layer intended for forming the diode cathode.
According to an embodiment of the present invention, the component is a MOS transistor including a plurality of source cells and the trenches are formed at the center of each of the cells.
According to an embodiment of the present invention, the component is a MOS transistor including a plurality of source cells and the trenches are formed between the cells.
According to an embodiment of the present invention, the component is a MOS transistor including a plurality of source cells and the trenches are formed at the center of the cells and between the cells.
According to an embodiment of the present invention, the surfaces of the trenches between cells are in contact with metallizations electrically connected to source metallizations of the cells.
The foregoing objects, features and advantages of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.